Project Summary/Abstract Background: Myeloproliferative Neoplasms (MPNs) are hematopoietic stem cell disorders in which myeloid progenitors expand excessively while retaining a normal ability to differentiate, leading to abnormal accumulation of mature myeloid cells. Currently, there are approximately 300,000 patients living with BCR/ABL-negative MPN, a heterogeneous class of the disease characterized by chronic evolution, unsatisfactory treatment strategies, and unpredictable progression to Acute Myeloid Leukemia (AML). While the genetic landscape of MPN patients over time is complicated, the one common denominator of all MPNs is chronic inflammation. Objective/Hypothesis: Our preliminary studies indicate that inflammation leads to DNA damage and genomic instability, contributing to the development of myeloproliferative disorder. We therefore propose to elucidate the molecular mechanisms. We hypothesize that chronic inflammation in the bone marrow (BM) niche: i) promotes proliferation and genomic instability in hematopoietic cells; and ii) cooperates with underlying genetic mutations to promote clonal expansion and selection, as well as the acquisition of de novo mutations, accelerating disease progression and transformation to AML. Specific Aims: (1) To determine whether an inflamed BM niche leads to clonal selection and disease progression in JAK2V617F-driven MPN; (2) To investigate the direct impact of an inflamed BM microenvironment on DNA damage and mutagenesis in JAK2V617F-driven MPN; and (3) To evaluate the impact of miR-155 suppression in MPN and disease progression. Study Design: We have developed an animal model where loss of RBPJ/Notch signaling in the BM microenvironment leads to chronic inflammation. We will utilize this model to study the role of inflammation on JAK2V617F-driven MPN. MPN cells will be exposed to an RBPJKO inflamed BM microenvironment using both in vivo transplantation and in vitro co-culture. We will investigate whether inflammation promotes clonal selection and disease progression in JAK2V617F-driven MPN using a colored barcode lentiviral tracking system. We will also explore whether inflammation directly causes DNA damage and mutagenesis over the course of JAK2V617F- driven MPN progression. Mathematical modeling will be employed to integrate this information with genomic data, to develop predictive tools for disease progression and to identify a temporal window of therapeutic intervention. Finally, we will examine the potential therapeutic efficacy of pharmacologic miR-155 blockade in preventing MPN disease progression and/or transformation. Cancer Relevance: This work will contribute to our understanding of the mechanisms of MPN disease progression and how inflammation cooperates with underlying genetic mutations such as JAK2V617F to drive disease. Ultimately, this will provide us with tools to better identify patients at risk for MPN progression and provide new therapeutic approaches for the prevention of disease progression and transformation to AML.